The present invention relates to the art of coating compositions.
It is known to apply clear and/or colored coatings to metallic and other articles compositions in order to improve durability and appearance, protect, finish and prevent oxidation of metals. For instance, the exterior panels of many automobiles and other outdoor articles are coated with a multilayer finish that contains: (1) a color coat or basecoat layer and (2) a clear coat layer. See, e.g., Blackburn et al., U.S. Pat. No. 4,732,791 (Mar. 22, 1988), which is incorporated herein by reference.
A common coating composition contains epoxy resins and polymers which contain cyclic anhydrides, such as maleic anhydride and itaconic anhydride polymers and copolymers. See, e.g., Corcoran, U.S. Pat. No. 4,816,500 (Mar. 28, 1989); Barsotti et al., U.S. Pat. No. 4,906,677 (Mar. 6, 1990); and Schimmel, U.S. Pat. No. 4,927,868 (May 22, 1990); and Mika & Bauer, "Curing Agents and Modifiers", Epoxy Resins Chemistry and Technology, 485-92 (Marcel Dekker, Inc. 1988), which are incorporated herein by reference. Optional ingredients in the composition are those which are well-known in the art of formulating surface coatings and include surfactants, flow control agents, thixotropic agents, fillers, anti-gassing agents, organic co-solvents, catalysts and other customary auxiliaries. The components are usually applied in an organic solvent and cured using a catalyst. These coatings are frequently used in outdoor applications such as clear and color coating on automobiles, storage tanks, rail cars, ships, bridges, utility structures and the like.
Public concerns over the emission of volatile organic compounds have made it desirable to coat such articles using a composition that has a very high solids content. At the same time, it is desirable for the resulting coatings to have at least about equivalent performance in terms of appearance and exterior durability. What are needed are new resins that can satisfy those concerns.